Secondary batteries employing aqueous metal halide solutions as electrolytes and free halogens as the electroactive material are extremely well known and have been extensively described in prior patents and literature. In secondary batteries of the foregoing type, a voltage is applied to the cell sufficient to result in the production of free halogen at the positive electrode. More recent patents dealing with the foregoing system have been concerned with the development of methods and apparatus for the efficient storage of the halogens formed during the charging phase of battery operation in a manner which would make the halogen available for reintroduction into the electrolyte during discharge of the battery. Thus, for example, Symons U.S. Pat. No. 3,713,888 describes a method and apparatus for converting the free halogen to halogen hydrate utilizing auxiliary apparatus external to the battery compartment and Zito U.S. Pat. No. 3,719,526 describes specially designed electrodes for entrapping the free halogens. The foregoing system as well as many others which are based on the same electrochemical action suffer from several disadvantages such as the potential emission of noxious halogen gases and the need for auxilliary apparatus.
Because of the foregoing drawbacks of systems based on halogens as the electroactive material, secondary batteries of the lead-acid type which are highly transportable and which require no auxilliary pumps or other apparatus for continuous charge and discharge are in widespread commercial use. Lead-acid type batteries are, however, highly poisonous and corrosive and the amount of energy stored per unit weight is relatively low. A need has long existed in the art for an energy storage method having the desirable features of lead-acid type batteries but which is capable of storing higher amounts of energy per unit weight and in which the content of the battery is less noxious and corrosive.